Method and apparatus for producing mobile radio signals

ABSTRACT

A method and device are provided for producing mobile radio signals, which utilize a direct conversion receiver, at least one first and one second local oscillator and one regenerative divider for processing signals according to different mobile radio standards. For generating the intermediate frequency for transmission according to at least one of the mobile radio standards, a division by four in addition to a division by three of the oscillator frequency is also possible.

BACKGROUND OF THE INVENTION

Over the course of recent years, wireless communication networks andmobile radio networks have developed to become an important component inthe communications infrastructure on a worldwide scale. As a result ofthe enormous demand for mobile radio capacity, various industry-standardcommunication technologies have been developed based on digitalmodulation techniques. Thus, for example, Code Division Multiple Access(CDMA), Time Division Multiple Access (TDMA) and frequency hoppingtechniques have been used in order to develop modern communicationsystems. Following parallel implementation of systems of these types, ithas proven to be advantageous to provide receivers which are capable ofoperating with one or more of these standard techniques. In order tomake this possible, it is necessary to provide a receiver which iscapable of receiving signals that have been modulated using differentmodulation techniques.

In Central Europe, in particular, but also in other regions of theworld, the GSM mobile radio system has been developed in this context,whereby different frequency ranges are made available within thissystem. The next few years will see the advent of the next generation ofmobile radio standard (UMTS, 3G) which will encompass additionalfrequency ranges.

From the standpoint of the manufacturer of terminal equipment, it is,therefore, becoming increasingly more difficult to guarantee signalgeneration for the different bands and standards at an acceptable levelof resource deployment and, conversely, to provide the correspondingreceive facilities; in particular, on the condition that the number ofoscillators used and their required tuning range should be kept as smallas possible.

Known receivers for processing signals employing different modulationstandards implement, for example, the double conversion receiverarchitecture. The double conversion receiver architecture isdistinguished by the fact that the received radio signal is converted toan intermediate frequency signal and the intermediate frequency signalis then converted downward into the base band. In addition, theintermediate frequency is also delivered to a gain check. However,double conversion receivers have the disadvantage that they require alarge number of circuitry components, which increases the costs, sizeand power draw of the receiver.

An alternative to these double conversion receivers is offered by directconversion receivers which have no intermediate frequency and,therefore, have no resource requirement with respect to filtering forthe intermediate frequency. For receiving, two-thirds or four-thirds ofthe oscillator frequency, which is used for downconversion of thereceive signal into the base band, is optionally generated from a firstlocal oscillator or from a second local oscillator via a regenerativedivider.

In this situation, for transmission, use is made of the fact that theregenerative divider also generates one third of the oscillatorfrequency as a “waste product”. This is subsequently IQ-modulated anddelivered to an offset PLL (phase-locked-loop) which steps it up to theactual transmit frequency. For the special UTMS application situation,the output signal is generated by mixing with the first local oscillatorsince, in this case, an amplitude-modulated signal must be present,which cannot be achieved with an offset PLL.

The disadvantage of this solution is the fact that the first localoscillator must have a broad tuning range from 1282.5 to 1452.5 MHz. Notonly is this difficult to implement but, under certain circumstances, iteven necessitates the use of two separate oscillators for the respectivesub-ranges. Furthermore, the offset PLL likewise contains twooscillators internally which make significant demands in terms of theirspace requirement.

An object of the present invention is, therefore, to provide a methodand an apparatus of the generic type in which as small a number ofoscillators as possible is used and the requisite tuning range is assmall as possible. As such, the solution should be capable of beingimplemented as cost-effectively and simply as possible.

SUMMARY OF THE INVENTION

Firstly, a method is provided for generating mobile radio signals via adirect conversion receiver, using at least one first and one secondlocal oscillator as well as a regenerative divider for dividing therespective oscillator frequency by three, for processing signals whichconform to different mobile radio standards, wherein an intermediatefrequency is produced during transmission for at least one of the mobileradio standards to be processed as a result of dividing one of the localoscillator frequencies by four.

A divider of this type having the factor 4 or a multiple thereof easilycan be integrated in silicon without a major resource requirement.

By preference, the method of the present invention is designed in such amanner that, optionally, a frequency division by three or four can takeplace.

Apart from the two local oscillators described, it is also possible touse a larger number of local oscillators. In addition, by preference,the local oscillator frequency IQ divided by three or by four ismodulated, whereby the modulated signal can be delivered jointly withone of the unmodulated local oscillator signals to an offset PLL or,alternatively, to a mixer.

The oscillator frequencies also can be higher than described above by aninteger factor, such as by a factor of 2, whereby a division of thefrequency by six or by eight would be required.

In addition, the present invention relates to an apparatus forgenerating mobile radio signals, for executing the method as describedabove.

Additional features and advantages of the present invention aredescribed in, and will be apparent from, the following DetailedDescription of the Invention and the Figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows an embodiment of an apparatus according to the teachings ofthe present invention.

FIG. 2 shows an alternative embodiment of the apparatus from FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an embodiment of an apparatus for generating mobile radiosignals in accordance with the present invention. In this situation, theapparatus includes a direct conversion receiver 2 which has nointermediate frequency and, therefore, has no resource requirement withrespect to filtering for the intermediate frequency. With regard to thereceive signal 4, the radio signals are GSM signals in the range 925 to960 MHz, DCS signals in the range 1805 to 1880 MHz and UMTS signals inthe range 2110 to 2170 MHz. In addition, the direct conversion receiver2 has an IQ output 6. For receiving, two-thirds or four-thirds of theoscillator frequency, which is used for downconversion of the receivesignal into the base band, is optionally generated from a first localoscillator 8 or from a second local oscillator 10 via a regenerativedivider 12. For transmission, use is made of the fact that theregenerative divider 12 also generates one-third of the oscillatorfrequency as a “waste product” which is IQ-modulated in an IQ modulator14 and subsequently delivered to an offset PLL 16. The offset PLL 16steps it up to the actual transmit frequency. For UMTS, the outputsignal is generated by mixing 20 with the first local oscillator 8since, in this case, an amplitude-modulated signal must be generated,which cannot be achieved with an offset PLL.

For transmission, the intermediate frequency for GSM and UMTS isproduced by the regenerative divider 12 by dividing the second localoscillator frequency 10 by three. For DCS, however, the intermediatefrequency is produced by dividing the second local oscillator frequency10 by four. In this manner, the first local oscillator 8 needs toprovide coverage in only a single range from 1330 to 1452.5 MHz and thesecond local oscillator 10 in a range from 1520 to 1627.5 MHz. Thenumber of oscillators used in this situation remains unchanged.

FIG. 2 shows an alternative embodiment of the apparatus from FIG. 1,whereby the same reference characters are used for the correspondingelements. In this case, the modulated intermediate frequency is filteredin a corresponding low-pass filter 22 and subsequently converted intothe transmit band not via an offset PLL as shown in FIG. 1 but by mixing24 with the first local oscillator 8. This makes it possible to transmitamplitude-modulated signals in the case of GSM and DCS, with the resultthat extensions of the standard, such as EDGE, for example, also can betaken into consideration. It is advantageous here that with the offsetPLL the latter's oscillators are also dispensed with, whereby filteringmeasures such as a diplexer 24 and an LO lock are provided in contrastto the embodiment shown in FIG. 1.

Signal generation for the different bands and standards is guaranteed atan acceptable level of resource deployment and, conversely, thecorresponding receive facilities are provided via the method presentedand the corresponding apparatus, the number of oscillators used andtheir required tuning range is kept as small as possible.

Although the present invention has been described with reference tospecific embodiments, those of skill in the are will recognize thatchanges may be made thereto without departing from the spirit and scopeof the present invention as set forth in the hereafter appended claims.

1. A method for producing mobile radio signals with a direct conversionreceiver that processes signals conforming to a plurality of differentmobile radio standards, the method comprising the steps of: respectivelyproviding local oscillator signals via at least one first and one secondlocal oscillator; producing, during transmission, an intermediatefrequency for a first mobile radio standard or a second mobile radiostandard using a regenerative divider by dividing the second localoscillator signal by three; producing, during transmission, anintermediate frequency for a third mobile radio standard using a dividerthat divides the second local oscillator signal by four; IQ-modulatingthe respective intermediate frequency; and delivering the resultingmodulated signal jointly with one of the respective local oscillatorsignals to at least one of an offset PLL and a mixer.
 2. The method forproducing mobile radio signals as claimed in claim 1, wherein the firstmobile radio standard is the Global System for Mobile Communications(GSM) standard, and the second mobile radio standard is the UniversalMobile Telecommunications System (UMTS) standard.
 3. The method forproducing mobile radio signals as claimed in claim 2, wherein the thirdmobile radio standard is the Digital Cellular System (DCS) standard. 4.An apparatus for producing mobile radio signals for a plurality ofdifferent mobile radio standards, comprising: a direct conversionreceiver; at least one first and one second local oscillator forrespectively producing local oscillator signals; a regenerative dividerthat produces an intermediate frequency during transmission for a firstmobile radio standard or a second mobile radio standard by dividing thesecond local oscillator signal by three; and a divider that produces anintermediate frequency during transmission for a third mobile radiostandard by dividing the second local oscillator signal by four; anIQ-modulator for modulating the intermediate frequencies; and at leastone of an offset phase-locked loop (PLL), for processing a modulatedsignal jointly with one of the respective local oscillator signals, anda mixer, for mixing a modulated signal with one of the respective localoscillator signals.
 5. An apparatus for producing mobile radio signalsas claimed in claim 4, wherein the first mobile radio standard is theGlobal System for Mobile Communications (GSM) standard, and the secondmobile radio standard is the Universal Mobile Telecommunications System(UMTS) standard.
 6. An apparatus for producing mobile radio signals asclaimed in claim 4, wherein the third mobile radio standard is theDigital Cellular System (DCS) standard.